1. Technical Field
The present invention relates to a gas laser oscillator apparatus mainly used for sheet-metal cutting and also relates to a laser gas replacement method used for the apparatus.
2. Background Art
A conventional laser oscillator apparatus is described with reference to FIG. 3. FIG. 3 shows a block diagram of a conventional gas laser oscillator apparatus.
The apparatus has gas piping path 903 for circulating laser gas and has blower 908 for circulating laser gas at a high speed. On gas piping path 903, the following components are disposed: supply-side electromagnetic valve 910 as a laser gas supply means for supplying laser gas; laser gas cylinder 930 disposed in the outside of the apparatus; usual discharge-side electromagnetic valve 912; rapid discharge-side electromagnetic valve 913; and discharge pump 914. In the structure above, usual discharge-side electromagnetic valve 912 is connected in series to flow restrictor 911. Flow restrictor 911 is the laser gas discharge means that discharges laser gas from gas piping path 903. A rotary pump, which is relatively inexpensive and has a simple structure, is generally employed for discharge pump 914.
In the structure above, discharge pump 914 of the laser gas discharge means for discharging laser gas from gas piping path 903 constantly works to supply gas piping path 903 with fresh laser gas at a predetermined ratio and to maintain the pressure in gas piping path 903 at a predetermined level. Under the condition, laser gas is supplied as follows. That is, usual discharge-side electromagnetic valve 912 connected in series with flow restrictor 911 is opened while rapid discharge-side electromagnetic valve 913 is closed. Opening and closing supply-side electromagnetic valve 910, which is disposed in the laser gas supply means that supplies laser gas while maintaining the pressure in gas piping path 903 at a predetermined level, allows laser gas cylinder 930 disposed outside the apparatus to supply fresh laser gas (see Patent Literature 1, for example).
The conventional gas laser oscillator apparatus described above, however, has the following problems.
To discharge laser gas, a vacuum pump has to keep operating during the operation of the apparatus. A rotary pump, which is generally employed for the vacuum pump, uses oil. This causes a back flow of oil mist from the discharge pump to the laser-gas flow passage. The back flow of oil mist can cause disturbance in discharge or mirror degradation in the gas laser oscillator apparatus and invite decreased laser output.
Such a low laser output causes instability in laser cutting and a poor cutting surface of a cutoff work, generating cutting failure. Preventing such a cutting failure caused by poor laser output due to the back flow of oil mist in the vacuum pump for discharging has been a pending problem.
Besides, the rotary pump is driven by a motor on electricity. The constant needs of power consumption have also been a problem in terms of energy saving.
The conventional art above discloses that the structure decreases oil mixed into the blower means by controlling the pressure of the laser-gas flow passage. However, with such a structure, preventing entry of oil mist into the rotary pump cannot be expected.